U.S. patent application number 11/015427 was filed with the patent office on 2006-08-17 for electrochemical impedance spectroscopy system and methods for determining spatial locations of defects.
This patent application is currently assigned to Bechtel BWXT Idaho, LLC. Invention is credited to Anne W. Glenn, David F. Glenn, Gretchen E. Matthern, W Alan Propp, Peter G. Shaw.
Application Number | 20060181262 11/015427 |
Document ID | / |
Family ID | 36758587 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060181262 |
Kind Code |
A1 |
Glenn; David F. ; et
al. |
August 17, 2006 |
ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY SYSTEM AND METHODS FOR
DETERMINING SPATIAL LOCATIONS OF DEFECTS
Abstract
A method and apparatus for determining spatial locations of
defects in a material are described. The method includes providing
a plurality of electrodes in contact with a material, applying a
sinusoidal voltage to a select number of the electrodes at a
predetermined frequency, determining gain and phase angle
measurements at other of the electrodes in response to applying the
sinusoidal voltage to the select number of electrodes, determining
impedance values from the gain and phase angle measurements,
computing an impedance spectrum for an area of the material from
the determined impedance values, and comparing the computed
impedance spectrum with a known impedance spectrum to identify
spatial locations of defects in the material.
Inventors: |
Glenn; David F.; (Idaho
Falls, ID) ; Matthern; Gretchen E.; (Idaho Falls,
ID) ; Propp; W Alan; (Idaho Falls, ID) ;
Glenn; Anne W.; (Idaho Falls, ID) ; Shaw; Peter
G.; (Idaho Falls, ID) |
Correspondence
Address: |
Alan D. Kirsch
P.O. Box 1625
Idaho Falls
ID
83415-3899
US
|
Assignee: |
Bechtel BWXT Idaho, LLC
|
Family ID: |
36758587 |
Appl. No.: |
11/015427 |
Filed: |
December 16, 2004 |
Current U.S.
Class: |
324/76.19 |
Current CPC
Class: |
G01N 33/383 20130101;
G01N 27/026 20130101 |
Class at
Publication: |
324/076.19 |
International
Class: |
G01R 23/00 20060101
G01R023/00 |
Goverment Interests
GOVERNMENT RIGHTS
[0001] The United States Government has rights in the following
invention pursuant to Contract No. DE-AC07-991D13727 between the
United States Department of Energy and Bechtel BWXT Idaho, LLC.
Claims
1. A method of determining defects in uncured concrete, prior to
curing of the concrete comprising: providing a plurality of
electrodes in contact with uncured concrete; applying a sinusoidal
voltage to a select number of the electrodes for each of a
plurality of source signal frequencies; determining gain and phase
angle measurements at receiving electrodes in response to applying
the sinusoidal voltage to the select number of electrodes;
determining impedance values from the gain and phase angle
measurements; computing an impedance spectrum for an area of the
material from the determined impedance values; and comparing the
computed impedance spectrum with a known impedance spectrum to
identify defects in the material, wherein defects in the uncured
concrete can be rectified before the concrete cures.
2. The method of claim 1, further comprising displaying the spatial
locations of the identified defects.
3. (canceled)
4. (canceled)
5. The method of claim 1, wherein the spatial locations of the
defects are determined by identifying a variation in impedance
value in the computed impedance spectrum relative to a known
impedance value of the known impedance spectrum.
6. The method of claim 1, wherein the defects that can be
determined include voids present in the material.
7. The method of claim 1, wherein shape and slope of the impedance
spectrum is related to physical and chemical characteristics of the
material.
8. The method of claim 1, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
9. The method of claim 1 and further comprising determining a
composition of a concrete material, wherein comparing the computed
impedance spectrum comprises comparing the computed impedance
spectrum with a known impedance spectrum to determine percentages
of concrete, sand, gravel, and water in the concrete material.
10. The method of claim 9, further comprising displaying the
composition of concrete material using at least one of a graphical
representation and a textual representation.
11. The method of claim 10, wherein shape and slope of the
impedance spectrum is related to physical and chemical
characteristics of the concrete material.
12. The method of claim 9, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
13. A system for determining the presence of defects in uncured
concrete, comprising: a plurality of electrodes configured to be
placed in contact with the concrete material, the plurality of
electrodes being spaced from each other; a voltage source
configured to apply a sinusoidal voltage at a predetermined
frequency to a select number of the electrodes; a current measuring
device coupled to other of the electrodes to measure a current
response in response to applying the sinusoidal voltage; and a
processor configured to: determine impedance measurements using the
applied sinusoidal voltage and the measured current response;
compute an impedance spectrum from the impedance measurements; and
compare the impedance spectrum with a known impedance spectrum to
identify defects in the concrete before the concrete cures.
14. The system of claim 13, wherein the processor is further
configured to display the composition of concrete material using at
least one of a graphical representation and a textual
representation.
15. A method of monitoring the stability of a bridge structure,
comprising: providing a plurality of spaced apart electrodes in
contact with the bridge structure; applying a voltage to a select
number of the electrodes, the voltage being applied at a
predetermined frequency; measuring a current response at other of
the electrodes in response to applying the voltage; determining
impedance measurements using the applied voltage and the measured
current response; computing an impedance spectrum from the
impedance measurements; and analyzing the computed impedance
spectrum relative to a known impedance spectrum to identify defects
of the bridge structure so as to determine the stability of the
bridge structure.
16. The method of claim 15, wherein the plurality of electrodes
comprise first and second electrode arrays, the second electrode
array being provided directly opposite the first electrode array,
and the defects comprise voids present in the bridge structure,
moisture penetrating the bridge structure, and micro-cracking of
the bridge structure.
17. The method of claim 15, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
18. A system for monitoring the stability of a bridge structure,
comprising: a plurality of spaced apart electrodes configured to be
placed in contact with the bridge structure; a voltage source
configured to apply a voltage at a predetermined frequency to a
select number of the electrodes; a current measuring device
configured to measure a current response at other of the electrodes
in response to applying the voltage; a processor configured to:
determine impedance measurements using the applied voltage and the
measured current response; compute an impedance spectrum from the
impedance measurements; and analyze the computed impedance spectrum
relative to a known impedance spectrum to identify defects of the
bridge structure so as to determine the stability of the bridge
structure.
19. The system of claim 18, wherein the plurality of electrodes
comprise first and second arrays of electrodes, the first array of
electrodes being provided directly opposite the second array of
electrodes.
20. The system of claim 18, wherein the defects comprise voids
present in the bridge structure, moisture penetrating the bridge
structure, and micro-cracking of the bridge structure.
21. The system of claim 18, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
22. A method of determining the weight of an object, comprising:
providing the object on a concrete structure; providing a plurality
of spaced apart electrodes in contact with the concrete structure;
applying a sinusoidal voltage to select ones of the electrodes at a
predetermined frequency; measuring a current response at other of
the electrodes in response to applying the sinusoidal voltage;
determining impedance measurements, of the concrete structure with
the object on the concrete structure, using the applied sinusoidal
voltage and the measured current response; computing an impedance
spectrum from the impedance measurements; and analyzing the
computed impedance spectrum with known impedance spectra for
differing weights to determine the weight of the object provided on
the concrete structure.
23. The method of claim 22, wherein the object comprises a
vehicle.
24. The method of claim 22, wherein the predetermined frequency is
selected from range of about 1 MHz to about 10 MHz.
25. A method of determining the weight of an object, comprising:
providing the object on a concrete structure; determining an
impedance spectrum of the concrete structure with the object on the
concrete structure; and comparing the determined impedance spectrum
with known impedance spectra for differing weights so as to
determine the weight of the object provided on the concrete
structure.
26. The method of claim 25, wherein determining the impedance
spectrum comprises: providing a plurality of spaced apart
electrodes in contact with the concrete structure; applying a
sinusoidal voltage to a select number of the electrodes at a
predetermined frequency; measuring a current response at other of
the electrodes in response to applying the sinusoidal voltage; and
determining impedance measurements using the applied sinusoidal
voltage and the measured current response.
27. The method of claim 26, wherein the object comprises a
vehicle.
28. The method of claim 26, wherein the predetermined frequency
comprises from about 1 MHz to about 10 MHz.
29. A system for determining the weight of an object, comprising: a
plurality of spaced apart electrodes configured to be in contact
with a concrete structure having a weight thereon; a voltage source
configured to apply a sinusoidal voltage to at least one of the
electrodes at a predetermined frequency; a current source
configured to measure a current response at other of the electrodes
in response to applying the sinusoidal voltage; a processor
configured to: determine impedance measurements, of the concrete
structure with the object on the concrete structure, using the
applied sinusoidal voltage and the measured current response;
compute an impedance spectrum from the impedance measurements; and
analyze the computed impedance spectrum with known impedance
spectra for differing weights to determine the weight of the object
provided on the concrete structure.
30. The system of claim 29, wherein the object comprises a
vehicle.
31. The system of claim 29, wherein the predetermined frequency is
selected from range of about 1 MHz to about 10 MHz.
32. A method of determining the speed of a vehicle, comprising:
contacting a first pair of spaced apart electrodes with a concrete
structure at a first location; contacting a second pair of spaced
apart electrodes with the concrete structure at a second location,
the first and second locations being separated by a predetermined
distance; applying a sinusoidal voltage to one of the electrodes of
both the first and second pairs of electrodes at a predetermined
frequency; causing the vehicle to move on the concrete structure;
determining impedance measurements at the first and second
locations of the concrete structure and in response to applying the
sinusoidal voltage; comparing the determined impedance measurements
with known impedance measurements of the concrete structure without
the vehicle moving on the concrete structure; monitoring impedance
variations at the first and second locations from the comparison;
recording first and second time instants for the monitored
impedance variations at the first and second locations,
respectively; determining an elapsed time period between the first
and second time instants; and computing the speed of the vehicle
using the elapsed time period and the predetermined distance
between the first and second locations.
33. The method of claim 32, wherein the predetermined frequency
comprises from about 1 MHz to about 10 MHz.
34. A method of determining a speed of a vehicle, comprising:
causing a vehicle to move between first and second locations on a
solid structure, the first and second locations being separated by
a predetermined distance; determining impedance measurements at the
first and second locations using electrochemical impedance
spectroscopy; comparing the determined impedance measurements with
known impedance measurements of the solid structure without the
vehicle moving on the solid structure; monitoring impedance
variations at the first and second locations; recording first and
second time instants for the monitored impedance variations at the
first and second locations, respectively; determining an elapsed
time period between the first and second time instants; and
computing the speed of the vehicle using the elapsed time period
and the predetermined distance between the first and second
locations.
35. The method of claim 34, wherein determining impedance
measurements at the first and second locations comprises: providing
a first set of opposing electrodes at the first location on the
solid structure; providing a second set of opposing electrodes at
the second location on the solid structure; applying a voltage to
one of electrodes of both the first and second sets of electrodes
at a predetermined frequency; measuring a current response at other
of the electrodes of the first and second sets of electrodes in
response to applying the voltage; and computing the impedance
measurements using the applied voltage and the measured current
response.
36. The method of claim 35, wherein applying a voltage comprises
applying a sinusoidal voltage.
37. The method of claim 35, wherein the solid structure comprises
concrete.
38. The method of claim 35, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
39. An electrochemical impedance spectroscopy system configured to
determine the speed of a vehicle moving on a solid structure,
comprising: a first set of opposing electrodes disposed to contact
a solid structure at a first location; a second set of opposing
electrodes disposed to contact the solid structure at a second
location, the first and second sets of electrodes being separated
by a predetermined distance; a voltage source configured to supply
voltage to a select number of electrodes of the first and second
sets of electrodes at a predetermined frequency; a processor
configured to: determine impedance measurements at the first and
second locations in response to applying the voltage to the select
number of electrodes of first and second sets of electrodes;
compare the determined impedance measurements with known impedance
measurements of the solid structure without the vehicle moving on
the solid structure; monitor impedance variations at the first and
second locations from the comparison; record first and second time
instants for the monitored impedance variations at the first and
second locations, respectively; determine an elapsed time period
between the first and second time instants; and compute the speed
of the vehicle using the elapsed time period and the predetermined
distance between the first and second locations.
40. The system of claim 39, wherein the solid structure comprises
concrete.
41. The system of claim 40, wherein the predetermined frequency is
selected from a range of about 1 MHz to about 10 MHz.
42. The system of claim 40, wherein the voltage source is a
sinusoidal voltage source.
Description
TECHNICAL FIELD
[0002] Aspects of the invention generally relate to electrochemical
impedance spectroscopy system and method for quality control to
visualize locations of anomalies in solid and semi-solid phase
conductive materials such as, for example, concrete.
BACKGROUND OF THE INVENTION
[0003] Concrete is a widely used construction material. As with all
construction materials, improved quality is desired for the
performance of a finished structure. Existing field quality control
techniques for concrete such as, for example, slump test, are used
to monitor bulk physical properties. Such quality control
techniques, however, do not directly measure the individual
physical or chemical components that affect the performance of the
concrete material. Microstructure of concrete can be of
considerable importance as it can govern the mechanical properties
and durability of the concrete. Such microstructure can have
significant influences on corrosion performance of reinforcing
steel in the concrete.
[0004] Current methods for measuring performance of concrete are
generally implemented after the material has been poured and
allowed to set. Under such conditions, corrections to the material
can be difficult to implement. A technique that could quantify the
quality of cements in the field prior to pouring could save time
and money.
[0005] Electrochemical impedance spectroscopy (EIS) has been
demonstrated to characterize electrochemical properties of
materials and their interfaces. Electrochemical impedance
spectroscopy is generally described in U.S. Pat. No. 5,370,776 to
Chen, U.S. Pat. No. 5,425,867 to Dawson et al., and U.S. Pat. No.
6,151,969 to Miller et al., all of which are incorporated by
reference in their entirety in this patent.
[0006] It would be desirable to have, in some embodiments, a
non-invasive system and method using the electrochemical impedance
spectroscopy to determine composition of a material to overcome the
above-identified drawbacks, in some embodiments. It would also be
desirable to use electrochemical impedance spectroscopy to measure
a variety of other physical phenomenon and overcome the time and
expense involved in measuring each of such physical phenomenon.
SUMMARY OF THE INVENTION
[0007] A need exists to use the electrochemical impedance
spectroscopy to interrogate a system of interest in order to
non-invasively determine a composition of the system. Needs also
exist to non-invasively determine the integrity of a structure,
weight of an object, or the speed of a vehicle using the principles
of electrochemical impedance spectroscopy.
[0008] Aspects of the invention generally relate to electrochemical
impedance spectroscopy systems and methods for quality control to
visualize locations of anomalies in solid and semi-solid phase
conductive materials such as, for example, concrete. Aspects of the
invention also relate to methods and systems for determining a
composition of a concrete material, methods and systems for
monitoring the stability of a bridge structure, methods and systems
for determining the weight of an object, and methods and systems
for determining the speed of a vehicle.
[0009] In some embodiments, a method and apparatus for determining
spatial locations of defects in a material are provided. The method
includes providing a plurality of electrodes in contact with a
material, applying a sinusoidal voltage to a select number of the
electrodes at a predetermined frequency, determining gain and phase
angle measurements at other of the electrodes in response to
applying the sinusoidal voltage to the select number of electrodes,
determining impedance values from the gain and phase angle
measurements, computing an impedance spectrum for an area of the
material from the determined impedance values, and comparing the
computed impedance spectrum with a known impedance spectrum to
identify spatial locations of defects in the material.
[0010] In other embodiments, a system and method for determining a
composition of a concrete material is described. A plurality of
electrodes is configured to be placed in contact with the concrete
material, the electrodes being spaced from each other. A voltage
source is configured to apply a sinusoidal voltage at a
predetermined frequency to a select number of the electrodes, and a
current measuring device is coupled to other electrodes to measure
a current response in response to applying the sinusoidal voltage.
A processor is configured to determine impedance measurements using
the applied sinusoidal voltage and the measured current response,
compute an impedance spectrum from the impedance measurements, and
compare the impedance spectrum with a known impedance spectrum to
determine percentages of concrete, sand, gravel, and water in the
concrete material.
[0011] In further embodiments, a method of monitoring the stability
of a bridge structure includes providing a plurality of spaced
apart electrodes in contact with the bridge structure, applying a
voltage to a select number of the electrodes, the voltage being
applied at a predetermined frequency, measuring a current response
at other of the electrodes in response to applying the voltage,
determining impedance measurements using the applied voltage and
the measured current response, computing an impedance spectrum from
the impedance measurements, and analyzing the computed impedance
spectrum relative to a known impedance spectrum to identify defects
of the bridge structure so as to determine the stability of the
bridge structure.
[0012] In other embodiments, a system for monitoring the stability
of a bridge structure includes a plurality of spaced apart
electrodes configured to be placed in contact with the bridge
structure, a voltage source configured to apply a voltage at a
predetermined frequency to a select number of the electrodes, and a
current measuring device configured to measure a current response
at other of the electrodes in response to applying the voltage. The
system also includes a processor configured to determine impedance
measurements using the applied voltage and the measured current
response, compute an impedance spectrum from the impedance
measurements, and analyze the computed impedance spectrum relative
to a known impedance spectrum to identify defects of the bridge
structure so as to determine the stability of the bridge
structure.
[0013] In other embodiments, a method of determining the weight of
an object includes providing the object on a concrete structure,
providing a plurality of spaced apart electrodes in contact with
the concrete structure, applying a sinusoidal voltage to select
ones of the electrodes at a predetermined frequency, measuring a
current response at other of the electrodes in response to applying
the sinusoidal voltage, determining impedance measurements, of the
concrete structure with the object on the concrete structure, using
the applied sinusoidal voltage and the measured current response,
computing an impedance spectrum from the impedance measurements,
and analyzing the computed impedance spectrum with known impedance
spectra for differing weights to determine the weight of the object
provided on the concrete structure.
[0014] In yet other embodiments, a system for determining the
weight of an object includes a plurality of spaced apart electrodes
configured to be in contact with a concrete structure having a
weight thereon, a voltage source configured to apply a sinusoidal
voltage to at least one of the electrodes at a predetermined
frequency, a current source configured to measure a current
response at other of the electrodes in response to applying the
sinusoidal voltage. The system also includes a processor configured
to determine impedance measurements of the concrete structure, with
the object on the concrete structure, using the applied sinusoidal
voltage and the measured current response, compute an impedance
spectrum from the impedance measurements, and analyze the computed
impedance spectrum with known impedance spectra for differing
weights to determine the weight of the object provided on the
concrete structure.
[0015] In further other embodiments, a method of determining the
speed of a vehicle includes contacting a first pair of spaced apart
electrodes with a concrete structure at a first location,
contacting a second pair of spaced apart electrodes with the
concrete structure at a second location, the first and second
locations being separated by a predetermined distance, applying a
sinusoidal voltage to one of the electrodes of both the first and
second pairs of electrodes at a predetermined frequency, causing
the vehicle to move on the concrete structure, determining
impedance measurements at the first and second locations of the
concrete structure and in response to applying the sinusoidal
voltage, comparing the determined impedance measurements with known
impedance measurements of the concrete structure without the
vehicle moving on the concrete structure, monitoring impedance
variations at the first and second locations from the comparison,
recording first and second time instants for the monitored
impedance variations at the first and second locations,
respectively, determining an elapsed time period between the first
and second time instants, and computing the speed of the vehicle
using the elapsed time period and the predetermined distance
between the first and second locations.
[0016] In other embodiments, an electrochemical impedance
spectroscopy system configured to determine the speed of a vehicle
moving on a solid structure includes a first set of opposing
electrodes disposed to contact a solid structure at a first
location, a second set of opposing electrodes disposed to contact
the solid structure at a second location, the first and second sets
of electrodes being separated by a predetermined distance, and a
voltage source configured to supply voltage to a select number of
electrodes of the first and second sets of electrodes at a
predetermined frequency. The system also includes a processor
configured to determine impedance measurements at the first and
second locations in response to applying the voltage to the select
number of electrodes of first and second sets of electrodes,
compare the determined impedance measurements with known impedance
measurements of the solid structure without the vehicle moving on
the solid structure, monitor impedance variations at the first and
second locations from the comparison, record first and second time
instants for the monitored impedance variations at the first and
second locations, respectively, determine an elapsed time period
between the first and second time instant, and compute the speed of
the vehicle using the elapsed time period and the predetermined
distance between the first and second locations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Preferred embodiments of the invention are described below
with reference to the following accompanying drawings.
[0018] FIG. 1A is a schematic view of a data acquisition and
analysis system for conducting the electrochemical impedance
analysis in accordance with various embodiments of the
invention.
[0019] FIG. 1B is a schematic of a fundamental approach of
electrochemical impedance spectroscopy in accordance with various
embodiments of the invention.
[0020] FIG. 2 is a schematic of a processing circuitry shown in
FIG. 1A.
[0021] FIG. 3 shows a representative impedance plot using
electrochemical impedance spectroscopy to determine differences in
the concentration of coarse aggregate in fresh concrete material in
accordance with one embodiment of the invention.
[0022] FIG. 4 shows a representative electrochemical impedance
spectroscopy plot during curing process of a concrete material
sample in accordance with one embodiment of the invention.
[0023] FIG. 5 shows a representative impedance plot for different
sections of a concrete material sample to detect differences in
gravel concentration in fully cured concrete in accordance with one
embodiment of the invention.
[0024] FIG. 6 shows a representative graph to detect water
intrusion into cured concrete in accordance with one embodiment of
the invention.
[0025] FIG. 7 shows a representative graph to determine the weight
of an object placed on a concrete material sample in accordance
with one embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] This disclosure of the invention is submitted in furtherance
of the constitutional purposes of the U.S. Patent Laws "to promote
the progress of science and useful arts" (Article 1, Section
8).
[0027] FIG. 1A is a schematic view of a data acquisition and
analysis system 100 for conducting the electrochemical impedance
analysis in accordance with various embodiments of the invention.
System 100 includes a material sample 102 (e.g., concrete) having a
plurality of electrodes 104, 106 provided in contact with the
sample 102, a voltage source 108, an output measuring device 110,
and a processing circuitry 112. The sample 102 can be any solid or
semi-solid conductive material.
[0028] System 100 can be used as a diagnostic tool to determine the
stability of concrete structures in the field. System 100 can also
be used during construction to find voids, to find poor
distribution of aggregate, to monitor curing of concrete, and to
continuously monitor performance and to diagnose problems (e.g.,
excessive vibration, etc.) in concrete structures.
[0029] The sample 102 can be a sample of fresh (e.g., uncured)
concrete material in one embodiment, and it can be a sample of
cured concrete material in other embodiments. The plurality of
electrodes 104, 106 can be metal electrodes provided in contact
with the sample 102. In one case, the plurality of electrodes 104
are provided on one side (e.g., side A) and the plurality of
electrodes 106 are provided on the other side (e.g., side B) of the
sample 102. The electrodes 104 can be considered to be a first
array or a first set of electrodes and the electrodes 106 can be
considered to be a second array or a second set of electrodes. The
electrodes 104 and 106 are equally spaced on side A and side B,
respectively, of the sample 102.
[0030] The voltage source 108 can be configured to provide an AC
potential to the sample 102 via electrodes 104. A small amplitude
AC potential is applied by the voltage source 108 to one of the
electrodes 104 buried on side A of the sample 102 in order to
determine an impedance spectrum for an area of the sample 102. The
amplitude and phase of the resulting source current with respect to
the applied source voltage is detected at one of the electrodes 106
that is provided directly across on side B of the sample 102 for
each of a plurality of source signal frequencies. The resulting
current can be detected by an output measuring device 110. In one
case, the output measuring device 110 can be a current measuring
device, such as, for example, an ammeter. Other current measuring
devices can be used. The source signal frequencies are selected
from a range of about 1 MHz to about 10 MHz. The shape, slope,
inflection points, and the range of frequency response depend on
the physical and chemical characteristics of the sample (e.g.,
sample 102) under evaluation. The total electrical current passing
through the concrete sample is assumed to be controlled by an
equivalent circuit. An exemplary equivalent circuit is discussed in
an article by Song et al., entitled "Equivalent Circuit Model for
AC Electrochemical Impedance Spectroscopy of Concrete," Cement and
Concrete Research, Aug. 7, 1990.
[0031] The amplitude and phase data for the resulting current at
each frequency and applied potential are used to calculate the
impedance for each frequency, including both the amplitude and
phase of that impedance. Impedance spectra for other sections of
the sample 102 are determined by applying a signal voltage to other
electrodes 104 and measuring the resulting current at electrodes
106. An impedance spectrum for the entirety of the sample 102 is
then computed. The complex impedance calculations and the computing
of the complete impedance spectrum can be performed under computer
control.
[0032] The processing circuitry 112 can be configured to perform
the impedance calculations for the resulting source current with
respect to each of the supplied voltages. The processing circuitry
112 can be configured to display the complete impedance spectrum of
the sample 102 so that various impedance values across various
sections of the sample 102 can be manually observed to determine
the composition of the sample 102. For example, one skilled in the
art can manually observe the variations in impedance values across
various sections of the sample and make a determination regarding
the composition of the sample 102. For example, the sample 102 can
include gravel, sand, cement, water, etc. and the impedance
spectrum can be used to determine the composition of such
materials. Based on the analysis of the impedance measurements
(e.g., increase/decrease in impedance at specific frequencies), a
determination of the location/distribution of aggregate, voids,
cracks, and other anomalies of a material sample (e.g., sample 102)
can be made.
[0033] System 100 can be used to visualize the spatial location of
material interfaces in a material sample (e.g., sample 102). The
material interfaces can result from different physical properties
(e.g., bulk material, aggregate, debris, voids, etc.).
Quantification of specific spectral properties (e.g., impedance
spectra) can be directly correlated with material type and location
of anomalies such as, for example, inhomogeneity of aggregate
within a bulk material sample.
[0034] In another embodiment, the processing circuitry 112 can also
configured to automatically determine the composition of the sample
102 by comparing the impedance spectrum with a predetermined
impedance spectrum. The processing circuitry 112 can also be
configured to determine the weight of an object received on a cured
concrete sample in one embodiment. In another embodiment, the
processing circuitry 112 can be configured to determine the speed
of an object moving across the cured concrete sample of a
predetermined length. Further details of the processing circuitry
112 are set forth with respect to FIG. 2.
[0035] FIG. 1B is a schematic of a fundamental approach of
electrochemical impedance spectroscopy in accordance with various
embodiments of the invention. A voltage source 108 is configured to
supply a voltage to the sample 102 and the resulting current is
measured using an output measuring device 110. Such details were
described above with respect to FIG. 1A and therefore are not
repeated.
[0036] FIG. 2 is an exemplary functional block diagram of the
processing circuitry 112 associated with the concrete sample 102
(FIG. 1A) in accordance with some embodiments of the invention. The
processing circuitry 112 includes a communications interface 202, a
processor 204, and a storage device 206 having a database 208.
[0037] The communications interface 202 can be configured to
communicate electronic data externally of the processing circuitry
112, for example, with respect to the output measuring device 110
(FIG. 1A). In some embodiments, the communications interface 202
may be configured to measure the resulting current and compute
impedance spectra without a need for the measuring device 110. The
communications interface 202 may comprise a parallel port, USB
port, EIO slot, network interface card, and/or other appropriate
configuration capable of communicating electronic data.
[0038] The processor 204 can be configured to process data to
compute impedance measurements and spectra (e.g., receive resulting
current measurements with respect to applied signal voltages) in
order to determine the composition of a concrete material sample
(e.g., sample 102), to determine the weight of an object received
by the sample 102, or to determine the speed of a vehicle passing
on a concrete structure (e.g., sample 102) of a predetermined
length. The processor 204 can be configured to determine such
parameters based on predetermined values and logic stored in the
storage device 206.
[0039] In one embodiment, the processor 204 may comprise circuitry
configured to execute computer software code. For example, the
processor 204 may be implemented as a microprocessor or other
structure configured to execute executable instructions of
programming including, for example, software and/or firmware
instructions. Other exemplary embodiments of the processor 204
include hardware logic, PGA, FPGA, ASIC, and/or other structures.
These examples of the processor 204 are for illustration, and other
configurations are possible for implementing operations discussed
herein.
[0040] The storage device 206 may be configured to store electronic
data, file systems having one or more electronic files, programming
such as executable instructions (e.g., software and/or firmware),
and/or other digital information and may include processor-usable
media. Processor-usable media includes any article of manufacture
that can contain, store, or maintain programming, data and/or
digital information for use by or in connection with an instruction
execution system including processing circuitry in the exemplary
embodiment. For example, exemplary processor-usable media may
include any one of physical media such as electronic, magnetic,
optical, electromagnetic, and infrared or semiconductor media. Some
more specific examples of processor-usable media include, but are
not limited to, a portable magnetic computer diskette, such as a
floppy diskette, zip disk, hard drive, random access memory, read
only memory, flash memory, cache memory, and/or other
configurations capable of storing programming, data, or other
digital information.
[0041] The storage device 206 includes a database 208 that can be
stored with information for determining the composition of the
sample 102 (FIG. 1A). Such information can include, for example,
the impedance values and impedance spectra and composition values
corresponding to such impedance values and impedance spectra. Upon
determining the impedance spectra using the resulting current as
described above, such impedance spectra may be correlated with the
impedance spectra stored in the database 208 in order to determine
the composition of the sample 102.
[0042] The database 208 can also be stored with information to
determine the weight of an object received by the sample 102. For
example, the database 208 can be stored with various impedance
spectra corresponding to various weights. Upon determining the
impedance spectra, such can be compared with the impedance spectra
stored in the database 208 in order to determine the weight of an
object received by the sample 102 in accordance with some
embodiments.
[0043] Information processed by the processing circuitry 112 can be
displayed on a display device 210. Information can be displayed in
one of a textual or graphical representation. Such displayed
information can include percentages of concrete, sand, gravel, and
water in the material (e.g., concrete).
[0044] FIG. 3 shows a representative impedance plot using
electrochemical impedance spectroscopy to determine differences in
the concentration of coarse aggregate present in a test sample
(e.g., sample 102 or fresh concrete material) in accordance with
one embodiment of the invention. The impedance spectra of FIG. 3
can be compared with known impedance spectra of a similar sample in
order to determine the composition of the test sample, thereby
enabling one to discern the differences in the concentration of
coarse aggregate in the test sample.
[0045] FIG. 4 shows a representative electrochemical impedance
spectroscopy plot during curing process of a concrete material
sample in accordance with one embodiment of the invention. In one
example, the sample 102 (FIG. 1A) can be uncured concrete material.
As illustrated in FIG. 4, the inventors have observed that the
impedance of the concrete material sample increases for the first
two hours of curing of the concrete material and decreases
thereafter. Such measured data and the impedance spectra can be
used to monitor the curing process of the concrete material
sample.
[0046] FIG. 5 shows a representative impedance plot for different
sections of a concrete material sample to detect differences in
gravel concentration in fully cured concrete in accordance with one
embodiment of the invention. In one case, the sample 102 (FIG. 1A)
can be a solid concrete slab. As illustrated in FIG. 5, the
inventors have observed that electrochemical impedance spectroscopy
can be used to detect differences in gravel concentration in fully
cured concrete.
[0047] FIG. 6 shows a representative graph to detect water
intrusion into cured concrete in accordance with one embodiment of
the invention. The inventors have added water to a material sample
(e.g., concrete slab or sample 102 of FIG. 1A) and monitored the
impedance of the sample at a frequency (e.g., 10 kHz) over a period
of time. The inventors have observed that water intrusion can be
detected in roads and bridge structures by monitoring the impedance
measurements.
[0048] FIG. 7 shows a representative graph to determine the weight
of an object placed on a concrete material sample in accordance
with one embodiment of the invention. A series of weights are
placed on the concrete material sample (e.g., sample 102 of FIG.
1A) and impedance values of concrete material sample at a
predetermined frequency (e.g., 1000 Hz) are measured for individual
ones of the weights on the sample. The measured impedance values
are compared with known impedance values of the sample with weights
placed thereon. The inventors have observed that when weights are
removed from the sample, the impedance values of the sample return
to a steady state condition (e.g., impedance values without the
added weight). Accordingly, the inventors have determined that by
placing a plurality of electrodes (e.g., electrodes 104, 106 of
FIG. 1A) on either sides of a concrete highway or roadway, the
number of vehicles passing a given point on the highway can be
determined. The inventors have also observed that the weight of
vehicles on the highway can be determined without the need for
expensive weighing scales. The inventors have also determined that
using electrochemical impedance spectroscopy as described with
respect to FIG. 1A, it is possible to (a) determine the speed of a
vehicle passing a section of a known length of a highway, and (b)
monitor the progressive damage caused to the concrete highway by
heavy vehicles.
EXAMPLE 1
[0049] In some embodiments, electrochemical impedance spectroscopy
can be used to determine spatial locations of defects in a material
using a system as shown in FIG. 1A. The method includes providing a
plurality of electrodes 104, 106 in contact with a material (e.g.,
sample 102), and applying a sinusoidal voltage to a select number
of the electrodes 104 at a predetermined frequency. Gain and phase
angle measurements are determined at other of the electrodes 106 in
response to applying the sinusoidal voltage to the select number of
electrodes. Impedance values are determined from the gain and phase
angle measurements using the processing circuitry 112. An impedance
spectrum is computed, using processing circuitry 112, for an area
of the material (e.g., sample 102) from the determined impedance
values, and the computed impedance spectrum is compared with a
known impedance spectrum to identify spatial locations of defects
in the material. The material can be concrete (e.g., wet, dry,
cured, uncured). The defects include voids present in the material,
separation of the material from a reinforcing bar, intrusion of
moisture into the material, micro-cracking of the material, and
freeze-thaw damage of the material.
[0050] A system for performing the task of Example 1 as described
above includes a plurality of electrodes 104, 106 (FIG. 1A), a
voltage source 108, and an output measuring device 110 (e.g.,
current measuring device). The system also includes a processing
circuitry 112 configured to perform the various tasks associated
with determining spatial locations of defects in a material as
described above.
EXAMPLE 2
[0051] In other embodiments, electrochemical impedance spectroscopy
can be used to monitor the stability of a bridge structure. The
method includes providing a plurality of spaced apart electrodes
104, 106 (FIG. 1A) in contact with the bridge structure, applying a
voltage to a select number of the electrodes 104, the voltage being
applied at a predetermined frequency. A current response is
measured (e.g., using output measuring device 110) at other of the
electrodes 106 in response to applying the voltage. The processing
circuitry 112 can be used to determine impedance measurements by
using the applied voltage and the measured current response. An
impedance spectrum is computed from the impedance measurements. The
computed impedance spectrum can be analyzed, either manually or
automatically using the processing circuitry 112, relative to a
known impedance spectrum to identify defects of the bridge
structure so as to determine the stability of the bridge structure.
Components of the system shown and described in FIG. 1A can be used
to monitor the stability of the bridge structure.
EXAMPLE 3
[0052] In other embodiments, electrochemical impedance spectroscopy
can be used to determine the weight of an object after placing the
object on a concrete structure (e.g., sample 102). A plurality of
spaced apart electrodes 104, 106 (FIG. 1A) are provided in contact
with the concrete structure. A sinusoidal voltage is applied to
select ones of the electrodes 104 at a predetermined frequency and
a current response is measured at other of the electrodes 106 in
response to applying the sinusoidal voltage. Impedance
measurements, of the concrete structure with the object on the
concrete structure, are made using the applied sinusoidal voltage
and the measured current response. An impedance spectrum is
computed from the impedance measurements. The impedance spectrum is
analyzed with known impedance spectra for differing weights to
determine the weight of the object provided on the concrete
structure. Such can be either performed by manually comparing the
impedance spectra or it can be automatically performed by the
processing circuitry 112. The storage device 206 (FIG. 2) can be
stored with a plurality of impedance spectra of the concrete sample
(e.g., sample 102) corresponding to various weights placed on the
concrete sample. The computed impedance spectrum can be compared
with the stored impedance spectra, and a determination can be made
regarding the weight of the object received on the concrete
sample.
EXAMPLE 4
[0053] In further embodiments, electrochemical impedance
spectroscopy can be used to determine the speed of a vehicle. The
vehicle can be made to pass on a given length of a concrete sample
(e.g., sample 102 of FIG. 1A). A first pair of spaced apart
electrodes (e.g., one of the electrodes 104 and one of the
electrodes 106) is configured to contact the concrete structure at
a first location (e.g., a first end of the sample 102 of
predetermined length). For example, of the first pair of
electrodes, one electrode can be considered to be one of the
electrodes 104 and the other of the electrodes can be considered to
be one of the electrodes 106, shown to be directly across the
electrode 104 in FIG. 1A.
[0054] A second pair of spaced apart electrodes (e.g., another of
the electrodes 104 and 106) is configured to contact the concrete
structure at a second location (e.g., another end opposite to the
one end of the sample 102). A sinusoidal voltage is applied to one
of the electrodes of both the first and second pairs of electrodes
at a predetermined frequency. The vehicle is caused to move on the
concrete structure between the first and second ends. Impedance
measurements are made at the first and second locations of the
concrete structure and in response to applying the sinusoidal
voltage. The measured impedance values are compared with known
impedance measurements of the concrete structure without the
vehicle moving on the concrete structure, and the impedance
variations at the first and second locations are determined from
the comparison. A first and second time instants are recorded for
the monitored impedance variations at the first and second
locations, respectively, and an elapsed time period between the
first and second time instants is determined. The speed of the
vehicle is computed using the elapsed time period and the
predetermined distance between the first and second locations.
[0055] Other applications of the electrochemical impedance
spectroscopy can include, for example, measuring the extent of
earthquake damage in concrete slabs in buildings, highways,
bridges, continuous monitoring of nuclear reactor containment of
vessels for structural integrity, continuous monitoring of loading
on concrete slabs (e.g., parking garages), quality control of fresh
concrete, locating voids and cracks in cured concrete, and
determining the extent of corrosion in reinforcing steel.
[0056] Electrochemical impedance spectroscopy can be advantageously
used as a tool for investigating the properties of materials. A
direct relationship exists between a real system and that of an
idealized model circuit consisting of discrete electrical
components. The impedance of an analog circuit model having, for
example, resistors, capacitors, and inductors, can approximate the
experimental impedance data. In such a circuit, a resistance can
represent a conductive path and a given resistor in the circuit can
account for the bulk conductivity of the material or one step in a
chemical reaction at the metal-solution interface. Capacitances and
inductances are generally associated with space charge
polarization. Changes in the magnitude of the various resistors,
inductances, and capacitances, over time can reflect changes in
specific properties of the materials being measured.
[0057] Electrochemical impedance spectroscopy techniques can
provide a way to monitor the curing process and long term
performance of cement structures, and could provide a simple,
inexpensive method to determine the relative permeability,
stability, and durability of cementitious systems. Electrochemical
impedance spectroscopy can also be used for jet grouting.
[0058] Electrochemical impedance spectroscopy has the potential to
measure or indicate for various physical and chemical properties of
materials including (a) measuring the size and content of aggregate
in concrete prior to, during, and after curing, (b) detecting voids
and cracks in concrete and other solid matrices, (c) measuring the
bulk conductivity of monolithic structures, and (d) identifying
regions of reactivity in solid phase reactive media such as, for
example, as used in permeable reactive barriers.
[0059] In compliance with the statute, the invention has been
described in language more or less specific as to structural and
methodical features. It is to be understood, however, that the
invention is not limited to the specific features shown and
described, since the means herein disclosed comprise preferred
forms of putting the invention into effect. The invention is,
therefore, claimed in any of its forms or modifications within the
proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
* * * * *